The present invention relates to a pressure sensor having a semiconductor body.
The purpose of sensors is to pick up events in a predominantly technical, although usually not electrical environment and to convert them into electrical signals. As is well known, the deformation of a strain gage caused by pressure influences its electric resistance. If the relationship between the deformation and the pressure is known, the unknown pressure can be determined by measuring the resistance change. Monocrystalline semiconductor material, particularly n-conducting silicon, is suited for this purpose because of its particular elasticity. The semiconductor body has the form of a diaphragm, on the surface of which the strain gage strip is prepared, generally in planar technology, by diffusing suitable doping substances. High-purity monocrystalline semiconductor material obeys Hook's law over a fairly wide range of strain values. The proportionality between the attacking force and the strain in the same direction remains effective up to an elongation of about 1%. In addition, the monocrystalline semiconductor material is free of hysteresis phenomena and remains elastic up to temperatures of several hundred degrees C. Furthermore, the piezo-resistance effect is particularly large in the monocrystalline semiconductor material. Therefore, correspondingly large changes of the resistivity are obtained by mechanical stress.
In one known embodiment of a miniature pressure transducer, a disc-shaped semiconductor body is provided, the flat sides of which extend preferably parallel to the (111)-plane of the crystal and which is provided at its surface with diffused-in electrically conductive zones, which serve as strain gage strips and can advantageously form four resistors of a bridge circuit. The silicon disc serves as a diaphragm and is surrounded by an enlarged rim. The resistor bands change their electric resistance as a function of the deflection of the diaphragm. The change of the resistance is a measure of the pressure acting on the diaphragm. See, for example, Philips Technische Rundschau 33, 1973/74, No. 1, pages 15 to 22.
It is an object of the present invention to improve the known pressure sensors, and, in particular, to simplify their design and allow for the setting of predetermined pressure ranges.